This invention relates generally to guiding an Intense Relativistic Electron Beam (IREB), and more particularly to using low energy electrons formed by a magnetic field into a channel through an ionizable gas to guide an IREB along a curved path.
IREBs are short (10's of nanoseconds) pulses of very high voltage (MeV) electrons and high current (10k's of Amperes). They are useful for radiography, laser pumping, microwave generation, beam propagation and basic physics research, etc. IREBs are typically formed by a cathode generating high power electrons towards an anode. Generators may either have a large magnet for focusing the electrons away from the anode and into a beam, or a thin metal foil for diverting the electrons from the anode, permitting them to pass down the channel. Additional information on these generators is provided by R. B. Miller, An Introduction to the Physics of Intense Charge Particle Beams, Plenum Press, New York, 1982. An IREB may also be generated using an ionized channel as taught by the copending patent application of C. Frost, G. Leifest and S. Shope entitled, "Ionized Channel Generation of an Intense Relativistic Electron Beam", Ser. No. 846,530, filed on Mar. 31, 1986, and assigned to the assignee of this application.
It is known that when an IREB beam is injected into a preionized channel, the beam space charge ejects plasma electrons, leaving an ion core which electrostatically attracts electrons to the ion channel.
D. S. Prono et al., "Electron-Beam Guiding and Phase-Mix Damping by Electrostatically Charged Wire," Phys. Rev. Lett. 51, 9, Aug. 29, 1983, pp. 723-726, discusses two experiments where a positive line charge was formed along a charged graphite wire supported on graphite foils. Prono found the charged wire to focus and damp the beam along the wire.
U.S. Pat. No. 4,507,614 issued to Prono et al. in 1985. This patent describes experiments with and without the charged wire. Beam transport was very poor without the wire.
W. E. Martin et al., "Electron-Beam Guiding and Phase-Mix Damping by a Laser-Ionized Channel," Phys. Rev. Lett. 54, 7, Feb. 18, 1985, pp. 685-688, reported the use of a laser-ionized channel for relativistic electron beam guiding, focusing and damping. They found the channel radius should be smaller than the beam radius for the radial focusing force to be anharmonic and thereby lead to desirable phase-mix damping of the transverse beam motion. They also found the electron beam density should be greater than the channel-ionization density to prevent beam instability.